This invention relates generally to the leaching of sulphide concentrates. Commercial bio-assisted heap leaching plants which are currently in operation treating mineral bearing sulphide ores such as secondary copper sulphide ores typically operate at temperatures in the range of 10° C. to 25° C. and rely on the exothermic oxidation of sulphide minerals to keep the temperature of the heap above ambient conditions. Addition of heat to the heaps by the burning of fuels is generally prohibitively expensive and, economically, is usually not justifiable, although some operations use heat generated during the thermal production of electricity to supplement heat generated within the heap.
Heap leaching carried out at relatively low temperatures, i.e. at a temperature of up to 25° C., limits the rate of sulphide mineral oxidation that can be achieved. The use of high temperatures increases the rate of sulphide mineral leaching. High temperatures, well above 25° C., may be achieved autogenously within the heap because of the exothermic oxidation of a high sulphide content in the ore.
Ores often do not contain very high levels of sulphide because the copper sulphide minerals are quite low in concentration. Although iron sulphides such as pyrrhotite and pyrite may also be present and undergo exothermic oxidation these are generally in low concentration as well.
Certain ores such as chalcopyrite ores cannot be leached at low temperatures. If the ore is low in concentration then sufficient heat will not be generated by exothermic oxidation to enable heap leaching to take place at all.
Bio-assisted heap leaching, as opposed to milling and flotation of copper sulphides to produce a copper concentrate, is the only economic process available, known to the applicant, for treating low-grade sulphide ores.